1. Field of the Invention
The present invention relates to a state information managing method which is able to manage easily state information of respective communication units and also reduce a communication traffic volume required for management of state information in a communication system wherein a plurality of communication units for exchanging data communication mutually are connected to a bus, and a communication system.
2. Description of the Prior Art
In a communication system in which a plurality of communication units are connected to a bus, respective communication units can exchange data communication mutually. At this time, since internal states of respective communication units are changed with the lapse of time, state information indicating the internal states have been managed by the communication units respectively.
As the state information management method, there has been such a method that, when the data management portion issues a state request to respective communication units, such respective communication units transmits a state response to the data management portion in response to the state request from the data management portion. However, according to this method, since the state request and the state response must be issued from respective communication units, an extensive communication traffic volume has been needed.
Therefore, there has been known the first method to reduce the communication traffic volume of the state request. In the first method, once the state request has been issued after a state information collecting destination has been identified clearly, the communication units which receive such state request have transmitted automatically state reports to the state information collecting destination subsequently every time when their states are changed. According to the first method, the communication traffic volume of the state request can be reduced.
However, according to the above first method, if reports of the state information are generated simultaneously from a plurality of communication units, collision of data has occurred. Therefore, for example, a means for avoiding such collision of data must be provided.
In addition, as the second method to reduce the communication traffic volume of the state request, there has been a method set forth in Patent Application Publication (KOKAI) Sho 64-24538, for example. According to this method set forth in Patent Application Publication (KOKAI) Sho 64-24538, the communication controller for sending out information sets a set of address data of own unit and to-be-sent information in the data portion in the certain communication message, and then plural information are sent out in sequence in compliance with procedure of deciding priority order which is decided by the address data. However, in the method set forth in Patent Application Publication (KOKAI) Sho 64-24538, the information request and the information collection are not carried out simultaneously.
Moreover, as the technology of this type in the prior art, there has been a system set forth in Patent Application Publication (KOKAI) Hei 3-38784. The system set forth in Patent Application Publication (KOKAI) Hei 3-38784 is the loop type communication system in which a plurality of communication frames are always circulated in serial.
Still more, the system set forth in Patent Application Publication (KOKAI) Sho 62-194759 is the communication system in which a plurality of nodes are connected like a loop and signals are transmitted in one way. In this communication system, a series of call setting procedures which are constructed by transmitting additional information necessary for call setting request for the transmitter side node issued from the transmitter side node and call setting allowance or call setting refuse and call setting are transmitted via packet transmission.
However, in the system set forth in Patent Application Publication (KOKAI) Sho 62-194759, individual collection is employed but batch collection is not employed. Therefore, according to the system, it has been difficult to reduce the communication traffic volume.